The background relating to vapor recovery systems is fully set forth in my U.S. Pat. No. 4,095,626, hereby incorporated by reference.
Briefly, in filling a vehicle's fuel tank at a service station, hydrocarbon vapors are displaced from the tank, and it is desirable to return these vapors to the underground fuel reservoir rather than discharge them into the atmosphere. My invention as disclosed in the aforementioned U.S. patent, accomplishes this by using a liquid jet gas pump. This pump employs a fuel flow therethrough to create a vacuum which draws the displaced vapors from a dispensing nozzle through a return conduit within the fuel hose back to the underground reservoir. However, in order to prevent vapor line blockage, the suction must be strong enough so that the vapors also entrain and carry along any liquid in the return line. It is extremely desirable that this returning liquid be detected, and if present in a sufficient amount, indicating too much suction, the dispensing nozzle automatically shuts off. For easy installation, it is also desirable that the liquid jet gas pump not require an external connection the atmosphere.